A lithium-ion battery has attracted attention as a battery used for hybrid vehicles and electric vehicles. The lithium-ion battery is produced by enclosing an internal structure (e.g., electrode) in a cylindrical or rectangular container (casing material), laser-welding a sealing lid (sealing material), and injecting an electrolyte solution into the container. An aluminum alloy that has a reduced weight, and allows integral press forming and laser welding has been used for forming the casing material and the sealing material.
When welding beads have locally become large and deep (i.e., when bead non-uniformity has occurred) when laser-welding the casing material and the sealing material, porosity may occur, or the internal structure may be thermally affected, or the beads may be locally removed to form a recess (i.e., the thickness of the sealed part decreases), whereby safety may be impaired, for example.
A JIS A1050 aluminum alloy has been employed as an aluminum alloy that exhibits excellent press formability and laser weldability. It has been proposed to limit the Ti content in a JIS A1050 aluminum alloy to 0.01% or less, or limit the viscosity in a liquid phase to 0.016 Pa·s by adjusting the Ti content and the B content in order to reduce the number of welding defects during laser welding.
An increase in strength and a reduction in thickness have been desired for an aluminum alloy sheet material for a lithium-ion battery in order to reduce the size and the weight of the lithium-ion battery, and use of a JIS A3003 aluminum alloy instead of a JIS A1050 aluminum alloy has been desired. However, since the JIS A3003 aluminum alloy has a high component content and includes a large amount of intermetallic compounds as compared with the JIS A1050 aluminum alloy, welding defects easily occur. Therefore, prompt measures to remedy this problem have been desired.